Possession
by lookaliveerin
Summary: Sherlock has been gone for so long and finally returns to find something different about John. When Sherlock discovers what's going on, he knows he has to try to save his friend or lose him again. Can he rescue John? - Post Reichenbach.
1. Chapter 1

Sherlock knew it would never be easy to return back to London and be re-united with his best friend who thought he was dead. It had been years and his friend had probably moved on with his life, recovered, but Sherlock hadn't. Before the fall, Sherlock made a promise to himself that he would make sure his friends were safe and then he would return in hopes of keeping them that way. Not so simple, really.  
First, Sherlock returned to greet Mrs Hudson, the woman that he respected so much and honestly thought of as a mother-figure in his life. He had never had that, not really. Sherlock did worry about her reaction, however it wasn't quite as bad as he expected, only coming out of the situation with a rolling-pin shaped mark on his arm. Mrs Hudson was stronger than anyone had given her credit.  
Next was Mycroft, because he realised that the man had probably already spotted Sherlock roaming around London recently, so didn't feel the need to visit him first. Although that prediction was correct, Mycroft still couldn't hide the overwhelming feeling of happiness to see his only family member back in his life.  
Lestrade's reaction was the funniest, and Sherlock couldn't hide the small, deep laugh in the silence of the empty parking lot as he watched the man frantically search for the item that had just been pick pocketed from him.  
Molly's reaction was more stunned into the fact that there was a mysterious man staring at her in the reflection of her locker mirror. She may have screamed.  
It was time to see John. Sherlock walked down the snowy road towards the restaurant Mycroft had told him John would be at.  
_"Do not go find him in there, Sherlock," Mycroft had warned. "I doubt he will want to be interrupted on his date."  
"Date?" Sherlock snapped back.  
"Yes, Sherlock," Mycroft rolled his eyes. "I know you're uneducated on the topic of relationships but John seems to have met someone who improved his mental health incredibly."  
Sherlock didn't listen to any more and had stormed out of the office to find his best friend.  
_Sherlock glanced through the large windows of the restaurant, seeing his friend sat at a table by himself. Oh, he was using a walking stick again. Was that guilt that Sherlock felt? His heart was racing as he opened the door and began walking across the restaurant towards the seat. Within a few seconds, he was stood with watery eyes staring at his friend right in front of the table.  
"That seat is taken," John said calmly as he began looking up. His gaze was fixed on Sherlock's eyes then when he continued speaking. "Oh, you're back."  
Not quite the reaction Sherlock was expecting.  
"I'm sorry John."  
"Hmm," John stared. "How'd you do it?"  
"I don't think here is the best place to-"  
"Yes, you're right." John interrupted. "Now if you don't mind, my girlfriend has arrived."  
Sherlock raised an eyebrow before glancing behind himself to see a blonde haired woman stood behind him with her eyes glaring into Sherlock's. He turned back to John.  
"Yes," Sherlock stuttered on his words a little bit. "I'm sorry, have a nice evening."  
Sherlock turned on his heels, walked back out of the restaurant and back to 221B Baker Street alone.

* * *

**What can you tell me about his girlfriend? – SH  
**Sherlock waited impatiently next to his phone, staring at the ceiling.  
**We don't know anything about her except her name: Mary Morstan –MH  
**Sherlock sighed in frustration and closed his eyes. Who was Mary Morstan and why didn't Mycroft know anything about her? Or rather, he probably did and refused to tell Sherlock.  
**Your dieting hasn't gone too well while I've been gone –SH  
I'm being serious, Sherlock. Do behave yourself. It's like she just appeared one day, no records of anything, not even her birth. I have been keeping my eye on her for John's safety while you were away. –MH  
**Sherlock groaned. Mycroft didn't need to protect John; that was what he had been doing. Sherlock was interested in Mary, how she'd changed John and what she'd done for him in the time of his absence. Why couldn't Mycroft get any information on her?  
**Where is she? – SH  
I'll send a car – MH  
**Within a few short minutes, Sherlock was sat in the black, dark car and driving to an unknown place. He was calculating the route to deduce where he was going and soon figured it out. He arrived at an abandoned warehouse soon and climbed out of the vehicle, approaching the metal gates that stood in place of a door. Sherlock pushed them open silently, hoping they wouldn't make any noise. The old warehouse smelt like damp and mould and it was full of dust with broken walls. There were a few grey stone steps leading up to another door which he then pressed his face closer to the door to listen to any sound behind the door.  
"What do we do?" that was John's voice.  
"Carry on," a female voice replied in an almost sarcastic tone.  
"I can't just avoid him, he's going to figure something's wrong eventually."  
Sherlock raised an eyebrow and listened more. John would be disappointed in him if he knew Sherlock was eavesdropping.  
"Well yes, he's not stupid."  
"So what then?" John snapped. "I just let him find out and go back to Baker Street?"  
"Exactly that."  
Sherlock heard the footsteps moving on the other side and rushed down the stairs quickly, not risking John finding him there and it making everything even worse. Luckily for him, the car had been waiting for Sherlock's return and he was soon on the way back to Baker Street.

* * *

Mrs Hudson was greeting Sherlock as soon as he returned from his investigation, but he had no time to listen to her.  
"I made a cake, Sherlock, don't you want some?" she shouted up the stairs as he bounded up them.  
"Maybe later, Mrs Hudson!"  
Sherlock knew she made food a lot when she had things on her mind, since the concentration she put into things to make them perfect made her forget about everything for an hour or so. Sherlock immediately opened his laptop and began to take matters into his own hands, researching who this Mary Morstan person was. He knew he would probably not have much luck getting any more information than Mycroft's people did, but his job was to protect John and she was definitely not sounding like somebody who could be good for him. Ironic, considering Sherlock pretended to be dead and lied to him a significant amount of times. He scrolled through tons of pages for what seemed like hours, but finally gave up, deciding that the internet proved useless. Sherlock sighed, closing his eyes and ruffling his hair.  
**Fancy getting back into cases? –Lestrade  
**Sherlock smiled at his phone slightly and typed a quick reply.  
**What've you got? –SH**

* * *

**A/N:**_ Opening chapters are not my strongest point so sorry for being boring. Next chapters will (hopefully) be much better! Please review if you've got the time, they help me improve my writing x  
_


	2. Chapter 2

Fully absorbed in his mind palace, Sherlock was stretched out on the couch in Baker Street, positioned in his usual thinking pose. Due to his mind being completely occupied with the case Lestrade had told him of, he didn't hear the footsteps that approached in an uncharacteristically quiet way, avoiding the creaking of one of the stairs. When Sherlock sensed another presence in the room, he snapped one eye open and saw John sat in his chair. The case could wait.  
"Sherlock," John greeted coldly with a nod of his head.  
"John." He sat up and waited for the conversation to resume, not wanting to rush into explanations if John wasn't ready, because John's emotions were very important to him. Silence had filled every dent and corner of the room, threatening to make the situation even more awkward than it already was.  
"So how did you manage it then?" The question was straightforward and blunt, so much so that Sherlock was stunned for a second before answering.  
"Moriarty wanted to kill you, Mrs Hudson, Lestrade..."  
"So you had to die instead," John continued for him. "I'm amazed you managed to keep quiet for this long."  
"You understand that if I had any other way to save you, I would have." Sherlock remembered the moment when Moriarty had shot himself after the brief conversation of not needing to die if he had him.  
"Oh Sherlock," John's voice was calm. "This is too fun."  
Sherlock raised an eyebrow and narrowed his eyes. People weren't meant to respond like that to the situation.  
John began to laugh to himself. "I'm sorry, I can't keep this up anymore." Within a short second, John blinked and suddenly was not John anymore. His friendly, comforting eyes became completely black.  
"If only you had an idea of how much pain John suffered while you were gone."  
"You're not John. Who are you?" Sherlock grabbed the person by the shoulders. "What are you?"  
"Careful now," they responded with a grin. "John's still here, he's just not in control of his own body right now. He's scared."  
Sherlock tightened his hands on the shoulders and his face became more threatening.  
"Calm down or I'll break his bones. I'll torture him, because whatever I do to myself, he will feel the pain of. Not to mention I can read his thoughts."  
"Who are you?" Sherlock repeated his question as he let go but didn't step away.  
"You can stick to calling me John, since I might stick around a while. You're interesting for a human. John thinks the world of you."  
Sherlock felt his heart sink knowing John was trapped inside his own body, finding out his friend was alive for so long secretly and discovering that in such a horrible way.  
"What are you?"  
"Ever heard of demons?" Fake-John walked towards the kitchen and flicked the button on the kettle.  
"I was never one to believe in things I cannot observe." Sherlock sat down in his chair.  
"Tea or coffee?" they smiled in response. "Never mind, John said you like coffee."  
Sherlock's eyes narrowed again as he watched Fake-John making the coffee correctly. They would only know that from what John was thinking.  
"Why did you possess him?" Sherlock asked after a few minutes of silently drinking coffee with the demon.  
Fake-John hesitated, drank another sip of their tea then answered with a straight face. "He doesn't want me to tell you."  
"Like that would stop you."  
"Don't pretend you know me, Mr Holmes. We have only just met."  
And for the first time in a long while, Sherlock really couldn't deduce anything about the demon. Nothing of importance, anyway.  
"How come you told me who you were so quickly?" he continued.  
"I thought it would be more fun to see your response to not being able to save your friend." They remarked with a small giggle. "It's funnier now I know that you pretending to _die_ just to save him last time."  
Sherlock stared at fake-John as they made their next comment with another small laugh. "John doesn't like me saying things like that. He's awfully defensive of you, Sherlock."  
"How long do you plan on staying and what will it take for you to leave?"  
The demon looked disappointed by his question. "Trying to get rid of me so soon? I expected you'd want to find as much as you can about me. But to answer your question, I'm going to stay for as long as I please and there's nothing you can do to make me leave. Sorry!"  
"Leave John alone and possess me instead," Sherlock practically demanded. "You'll see all of the observations I see, understand the deductions I make."  
Fake-John seemed to consider this for a minute however shook their head slowly. "No... Maybe later."  
"Fine." Sherlock snapped. "I have a case to solve."  
Sherlock stood from his chair, placed the empty coffee mug on the table (after stepping across it, of course), then recommenced his earlier thoughts from the comfort of the couch.  
Before fading away to his mind palace, Sherlock heard Fake-John say something in an almost whisper.  
"John says you did this a lot."

* * *

"Fingernails!" Sherlock yelled, his hands thrown into the air and eyes wide open. "John, call Lestrade."  
The realisation that John was not _actually_ John hit him after he made the instruction, and he looked to see the man sat in his chair staring at him with a small smile growing on his face.  
"Sure." He answered, picking up the phone and dialling the number.  
Sherlock raised an eyebrow but put his coat and scarf on.  
"Lestrade," Fake-John greeted on the phone. "Yes, it's John."  
There was a moment of silence as he was listening to the reply before interrupting. "Yeah, Sherlock solved it, something about fingernails apparently. We'll be over in a few minutes."  
Fake-John hung up the phone and threw a jacket on quickly before looking at Sherlock expectantly.  
"Well? Come on."  
"Why do you want to come with me?" Sherlock questioned.  
"I'm intrigued." Fake-John shrugged his shoulders. "Now let's go, I'd like to see what this case is."  
The pair left Baker street quickly and were in a taxi on the way to meet Lestrade when Sherlock caught Fake-John watching him.  
"What is it?"  
"I have to admit," he explained. "I didn't expect you to be taking all of this in your stride. I've admitted that I am possessing your friend that you haven't seen for ages and yet you're quite fine with that."  
"It's interesting." Sherlock looked out of the window and avoided further conversation.  
"Quite."

* * *

Sherlock almost ran to Lestrade's office, bouncing up the stairs two at a time with Fake-John following close behind him.  
"Sherlock," Lestrade smiled as he walked in. Sherlock quickly deduced that the smile was a genuinely happy to see him, but he had tired eyes and his skin was paler than usual. There was a fresh cup of coffee on the desk but dry marks around the cup so he had already drank at least one within the past hour. Lestrade was lacking in sleep, but not due to any family or work related matters. No, this was because he was still trying to get his head around the return of his dead friend.  
"John, it's good to see you. It's been a while," he greeted.  
"And you," Fake-John replied with a quick grin.  
"So, fingernails?"  
Sherlock's eyes flashed from Fake-John to Lestrade and he began to reveal the mystery behind the case. "Kara bit her fingernails, it was something she did when she was nervous or stressed, but it was only a recent habit so she knew something was coming, something was going to happen to her. Obviously it was murder, we established that, but it was pre-meditated and provoked."  
"Provoked? How do you know that?" Lestrade asked with a raised eyebrow. Sherlock could feel Fake-John's eyes staring at him.  
"She was addicted to gambling and ended up running into financial problems, so she had to borrow some money from wherever she could get it." He explained. "Stupidly and desperately, she picked the first person she found who happened to give her a large interest rate with a short payback time and unfortunately it cost her life. The guy you're looking for is Robert Willison."  
"Thanks, Sherlock." Lestrade nodded his head and began dialling a number. "What did I do without you to solve these cases?"  
Sherlock grinned before leaving the office with Fake-John who seemed quiet. They walked down the stairs to leave and eventually he spoke.  
"John was right, that is quite cool."  
Sherlock laughed a little bit. "I'm flattered."

* * *

**A/N: **_So the mystery is revealed as to why John is acting differently! Little note that I'm so happy with the response I'm getting from this, and reviews will be very much appreciated, so if you've got the time to write one and something to say, please do! I'll try get the next chapter up within a week. x_


End file.
